120 строки
2.6 KiB
C#
120 строки
2.6 KiB
C#
using System;
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using System.Reflection;
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using System.Windows.Input;
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namespace Xamarin.Forms
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{
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public sealed class Command<T> : Command
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{
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public Command(Action<T> execute)
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: base(o =>
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{
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if (IsValidParameter(o))
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{
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execute((T)o);
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}
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})
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{
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if (execute == null)
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{
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throw new ArgumentNullException(nameof(execute));
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}
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}
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public Command(Action<T> execute, Func<T, bool> canExecute)
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: base(o =>
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{
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if (IsValidParameter(o))
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{
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execute((T)o);
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}
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}, o => IsValidParameter(o) && canExecute((T)o))
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{
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if (execute == null)
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throw new ArgumentNullException(nameof(execute));
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if (canExecute == null)
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throw new ArgumentNullException(nameof(canExecute));
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}
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static bool IsValidParameter(object o)
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{
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if (o != null)
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{
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// The parameter isn't null, so we don't have to worry whether null is a valid option
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return o is T;
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}
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var t = typeof(T);
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// The parameter is null. Is T Nullable?
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if (Nullable.GetUnderlyingType(t) != null)
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{
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return true;
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}
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// Not a Nullable, if it's a value type then null is not valid
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return !t.GetTypeInfo().IsValueType;
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}
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}
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public class Command : ICommand
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{
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readonly Func<object, bool> _canExecute;
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readonly Action<object> _execute;
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readonly WeakEventManager _weakEventManager = new WeakEventManager();
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public Command(Action<object> execute)
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{
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if (execute == null)
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throw new ArgumentNullException(nameof(execute));
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_execute = execute;
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}
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public Command(Action execute) : this(o => execute())
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{
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if (execute == null)
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throw new ArgumentNullException(nameof(execute));
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}
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public Command(Action<object> execute, Func<object, bool> canExecute) : this(execute)
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{
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if (canExecute == null)
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throw new ArgumentNullException(nameof(canExecute));
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_canExecute = canExecute;
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}
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public Command(Action execute, Func<bool> canExecute) : this(o => execute(), o => canExecute())
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{
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if (execute == null)
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throw new ArgumentNullException(nameof(execute));
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if (canExecute == null)
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throw new ArgumentNullException(nameof(canExecute));
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}
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public bool CanExecute(object parameter)
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{
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if (_canExecute != null)
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return _canExecute(parameter);
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return true;
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}
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public event EventHandler CanExecuteChanged
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{
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add { _weakEventManager.AddEventHandler(nameof(CanExecuteChanged), value); }
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remove { _weakEventManager.RemoveEventHandler(nameof(CanExecuteChanged), value); }
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}
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public void Execute(object parameter)
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{
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_execute(parameter);
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}
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public void ChangeCanExecute()
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{
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_weakEventManager.HandleEvent(this, EventArgs.Empty, nameof(CanExecuteChanged));
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}
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}
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} |